My 51 is enclosed with two failures but I don't know if heat was the culprit. A small amount of oil gets past the sprocket seal. I DO like not having oil all over the bike and the garage floor, and I will carry a spare belt with me in the future. The belt can be swapped without loosening the tranny just by useing the "big washer and adjuster nut" trick to pull the basket out far enough to get the belt over the sprocket (my sprocket has no tin flange). I'm happy with the final drive ratio using the 8mm belt with a 39 tooth sprocket 62clutch shell 24 tranny and 51 rear sp. I usually cruise about 65. Mike

51hog
I've got a 11MM with a 22 tooth tranny drive sprocket and was just on I 95 doing 70-75 and she purred like a kitten .I don't use a cover gasket on the outer primary and the hole from where the breather was is open, so it gets some air .Here's a photo of how my breather is set up.

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john HD wrote:so is it the consensus that modern belts do not need ventilation?

they can be run enclosed in stock primary cases?

the last belt setup i ran was open and had an affinity for picking up pieces of gravel and blowing holes in the belt... that is why i got rid of it.

john

And so the saying goes...Yes, I have heard that ventilation increases belt life.

I run mine open COMPLETELY...Ugh you say...I plan on installing a belt guard real soon. Lately I've had a thought of falling and that belt/clutch basket tearing up my leg! Udly! Running her open does expose her to small pebbles, dirt etc. all which causes damage to the pully teeth, I admit. I'm changing it, to some degree!

My bud runs his entirely closed and he hammers that motorcycle...no problem to date but I think it's a given he'll end up with a broken belt at ome time or another most likely due to his abuse but I'm thinking prolonged heat buildup in that primary will play a factor also...just speculation, no hard evidence to confirm that theory!

I think any method you use to vent is encouraged. Yes, over the past 30 years I broke one belt back in the 70's!!!! I got a bit tippsy, OK...I was drunk and I NEVER drink and drive any longer, honest. I fell doing about 30 to 40MPH I think (!) and landed in gravel, skidded on my left side and put a hole in my aluminum primary just south of the clutch inspection cover...needless to say, that gravel tore that belt to pieces and destroyed the pully! My bad! But it was hell pushing her the distance I did...this was before cell phones ad people just didn't approve of knocking on their door if you were a biker in those days!

" The belt can be swapped without loosening the tranny just by useing the "big washer and adjuster nut" trick to pull the basket out far enough to get the belt over the sprocket (my sprocket has no tin flange). I'm happy with the final drive ratio using the 8mm belt with a 39 tooth sprocket 62clutch shell 24 tranny and 51 rear sp. I usually cruise about 65. Mike[/quote]

Yup, that's what I'm talking about...easy as hell to change a belt...I also use the BIG WASHER method, I carry one in my tool kit. Just removed a belt last week and this was as simple as it got...I also run the BDL type and its the 39/62 and mine also purrs so smooth!

That is a pretty slick way of changing the vent Fourthgear--
I am not going to cut the CC vent tube. I will use a piece of rubber tubing to route it back out of the primary, just n case I want to revert to the chain setup at a later date. I will attempt to mist my rear chain with it. I turned the primary oiler off and do not even get a drip out of the primary case, and needed to manually oil the primary chain.
For the time being, I don't think that oil will be a problem.

My primary case will be closed and vented with a couple of louvers on the inner case. There will be no gasket between the cases. My derby and inspection cover will have parts of the lower gaskets removed for ventilation.
I am going to order the 31-47 tooth 11 mm drive kit with a 24 tooth tranny sprocket, I will be 5.93 mph faster than stock at the same rpm of the engine.
Thanks all for all of the advice and tips. It is great that everyone is willing to take their time to help out......
Dale

Fourthgear thereÃ¢â‚¬â„¢s an alternative to your breather port. On the back of the right case to the upper left above the oil pump is a freeze out plug. ThatÃ¢â‚¬â„¢s the same passageway for the breather. Use a standard HD 5/16X3/4X1/4 spacer with gasket on the engine side. Pull the freeze out plug and put a Ã‚Â¼Ã¢â‚¬Â pipe tap in it. Put one Ã‚Â¼ NPTXhose barb adaptor in it with a piece of hose. Attach one of the modern 70Ã¢â‚¬â„¢s something breather thingies to the end and your set.
For the rest of you that have had a hand in this post. All a guy with past knowledge can say is simple. Run one of these over priced revolving torpedoes and you can get to use all them cool tools in the photos of the Tool Kit post and this includes credit cards just like JohnÃ¢â‚¬â„¢s. YouÃ¢â‚¬â„¢ve got to admit that Harley is a labor of love or torture. ItÃ¢â‚¬â„¢s up to you which road you want to take. 1950bobber itÃ¢â‚¬â„¢s nice to see that someoneÃ¢â‚¬â„¢s king around the forum. I was starting wonder. Bob

I am now testing the new 11mm BDL 1.5 inch belt drive in my closed primary that isn't closed yet. Just want to make sure that it tracks correctly, and that the tension or lack there of stays like I want it.
Right now, I can push down on the belt with about 3 lbs pressure and deflect it 3/4 inch. While the engine is running at about 2000 rpm out of gear, the belt flutters up and down a total of about 3/4 inch.
Belt is tracking in the center of the engine pulley, and to the outside of the clutch drum.
A LOT of my vibrations at cruise went away when I installed the belt.
Maybe because the rpm of engine is slower at the same speed as before.
I have not ridden it far enough yet to heat up the pulleys so I don't know how tight the belt will get when they expand.

I used a piece of vinyl tubing to route the CC vent to the outside of the chain case. There is a slight trap in it and the trap will fill with oil and hopefully will just sea saw back and forth and spit out the extra when needed. Maybe it will stop the dust from getting drawn into the crank case..

I have put on about 60 miles on the new belt with the outer tin off. The front pulley gets warm from the engine. The rear pulley is just warm to the touch. There is no noticeable change in belt tension after a 30 mile ride. I expect the pulleys and the belt to warm up a little after the outer tin is in place.
I think the gearing using the 31-47 tooth 11 mm drive kit with a 24 tooth tranny sprocket is a little high around town. Engine is lugging in fourth gear at 45 mph (We have a lot of 40-45mph up here). Running in third gear is almost perfect with the exception of the whine. I haven't been to the mountains yet to see if she has enough power to hold speed climbing hills. I can still accelerate up an overpass at highway speed. The vibrations that I feel now at 65-70mph appear to be Power pulses from the firing cylinders.
I may try a 23 tooth tranny sprocket.....

Nice slow lope at 60. Almost lugging. Can definitely feel each piston fire.
65 mph is better, and 70 is perfect---about 1/4 or less throttle to hold it there M35TP. Acceleration on flat ground is acceptable from 65 to 80 where it pretty much just levels off then slowly creeps to about 90 at WOT.

Can run 70 in 3rd and engine still sounds good but vibrations are more than I like.

That's tall, in third and fourth. I think I'll remove my 26T and install the 25 on the trans. The motor is 31 the clutch is 47. 1-1/2" x 11mm Primo.
Or, maybe I'll run the 26T trans. to be able to report back what it was like at 62-63 mph. Thanks for the dial-in on road feel.